1. Field of the Invention
This invention relates generally to carriers and viscosifiers, and more particularly to a high carrying capacity temperature-stable breakable gel of selectable viscosity capable of performing as efficient carriers of solids and particulate matter, as well as semi-solids and liquids.
2. Background Art
Rheological agents, thickening mediums with many applications, have long been used. Virtually any purpose that is enhanced by water losing some of its free-flowing characteristics is a candidate for the utilization of thickening agents or viscosifiers.
Hundreds of U.S. Patents have been granted for thickened water and hydrocarbons in the form of guar, cellulose and its derivatives, resins, polysaccharides, starches, oleaginous fluids, amine oxides, styrenes, organic phosphate esters, polymers cross-linked with many products including amines, zirconium, and titanium based cross-linkers, boron and ester forming compounds, and combinations and derivatives of all of these. Fracturing products also include tackifying compounds to coat proppants, fibrous materials, magnetized materials, and single to multiple configurations of proppants with even those composed of both man-made products and natural materials, even peanut hulls. Gel breakers have been patented including temperature and alkali metal breakers, enzyme breakers, staged breakers, multiple breakers, encapsulated breakers, quaternary ammonium halide salts, and other compounds are commonly used not only as well drilling and fracturing fluids but also as masks in textile and carpet printing to screen-off those areas from applied dyes.
Hand lotions, shampoos and cosmetics are commonly no more than thickened water which becomes a carrier for desired additives. Fire fighting and prevention are greatly enhanced by the use of thickened or gelled water. Most of these applications are rather straightforward in their utilization of thickened waters; thicken the water either before or after the addition of the desired additives with the result being ready for the intended use. However the need for the elimination of the thickening is desirous in many instances.
Since water has insufficient viscosity and carrying capacity to efficiently suspend heavier particulates and other matter to be moved, transported, or stored, additives of many kinds have long been used to increase water-use efficiency in petroleum and water well drilling, workover, completion and distribution. Materials such as cuttings and debris, including sand, must be carried out of boreholes during drilling and completion processes. Additionally, increased viscosity water has long been used to carry various additives and other matter into and out of wells including solids such as sand and gravel; these are used to increase drilling efficiency and production output. Similar suspension products are also useful for distribution and storage.
Water thickening agents have long been known to those skilled in the art. In well drilling for example, the addition of desired materials allow thickened water to be used for blowout prevention and as lubricants for the drill string but they serve many other uses. They are additionally used as viscosifiers, rheological agents and carriers for propping agents (proppants) used in well fracturing, particulates such as gravel packs, and other materials including, but not limited to, GILSONITE® (a naturally occurring hydrocarbon resin that is similar in appearance to coal or hard asphalt), sulfonated asphalts, graphite, surfactants and other materials which may serve as lubricants, for diversion agents, and for plugging fine holes in the strata such as shale, thus controlling fluid “spurt” and thief zone loss. Currently viscosity-increasing agents are also added to water so that it will effectively function as a particulate carrier as well as a carrier for additives that prevent clay swelling, and a myriad of other complications associated with drilling, completion, production and distribution. Viscosifying agents include conventional linear gels such as guar gums and derivatives including, but not limited to carboxymethylhydroxypropyl guar, hydroxypropyl guar, carboxymethyl guar, xanthates, many cellulose formulations such as hydroxyethyl cellulose (HEC), and carboxymethylhydroxyethyl cellulose, hydrolyzed polyacrylamide, polysaccharides, and other compositions together commonly collectively referred to as viscosifiers.
Guar and cellulose type viscosifiers are relatively slow to reach their effective viscosity and are notorious for being virtually unusable in cold water. Most require the use of hot water if they are to be rapidly and efficiently dissolved. Following their slow hydration and the resultant maximum thickening of these previous art viscosifiers, they are still lacking in their ability to support and efficiently carry cuttings or other materials, especially during a pause or cessation of fluid movement whatever the cause. In such cases, entrained matter often settles due to failure of carrier support and suspension capacity. This can result in tremendous time and economic loss.
Typical viscosifiers of prior art are particularly susceptible to the boycott effect which compromises their sag or carrying capacity in deviated wells, particularly in horizontal boreholes. The resultant accumulations may block the well or cause seizure of the drill stem especially in deviated wells such as horizontal boreholes where particulate accumulation is notorious for causing drill stem seizure and loss of wells. Likewise in distribution, particulates may settle to the bottoms of pipelines, and shipping and storage containers. In all uses, high carrying capacity without excessive viscosity is vital because higher viscosity without carrying capacity results only in higher pressures being required for product movement.
Guar, xanthane, cellulose and their derivatives and similar based carriers may change viscosity as they progress down hole. Increased temperatures, dilution, and the presence of other materials often compromise such carriers causing failure. The addition of significantly more carrier may be required to maintain the desired viscosity if the returns are to be recirculated. Almost all of the above noted carriers are subject to failure at even mild temperature increases commonly encountered in drilling to any significant depth. Virtually all such materials lose as much as 60% efficiency with as little as 400° F. rise in downhole temperature commonly experienced.
Viscosifying agents are commonly used to formulate carriers of various proppants used in attempts to establish permanent porosity in fractured strata and maintain openings in the pore throats. The use of many types of viscosifiers is currently being phased out of use because of the difficulty or impossibility of removing them after they have served their transport purpose and also because of their toxicity and possible aquifer and groundwater contamination
Removal of additives such as viscosifiers, commonly referred to as “formation healing,” is vital. After serving their intended purpose, the inherent carrier residue of the linear gels such as the guar and cellulose type is often difficult, and frequently impossible, to remove. They effectively bond to strata and many commonly used proppants, especially silica based materials. Their viscosity can be decreased by further dilution with large quantities of water, which aids in their removal. Injection of enzyme breakers is helpful but results are usually slow and frequently meet with limited effect. The residual carriers are subject to microbial action, which adds further complications. Ineffective removal and subsequent accumulation of prior art viscosifiers commonly spawns the occlusion of the very fractures and pores into which they were purposely injected to open. Prior to the present invention, these were commonly difficult to impossible to clean up. Carrier component accumulation commonly compromises fluid flow and therefore production efficiency.
Cross-linked gels do not invade the formation as deeply as linear gels, but they do develop a very concentrated buildup near the fracture face. Carrier presence may contribute to the tendency for sand and gravel to pack and accumulate, thus forming viscosifier reinforced “sand bridges” which can occlude casing, tubing, and/or flow lines primarily because they are so difficult to remove.
In water well drilling, the injection of carriers containing toxic or other agents deleterious to health may require lengthy flushing of the well before the produced water may be utilized. Many are virtually impossible to remove. Many jurisdictions have already banned the use of such.
Not only are some organic viscosifiers difficult to remove from the subterranean strata, when returned to the surface, many of these organic additives such as the guars may have significant negative environmental impact. They must be disposed of properly creating permit, handling and transportation problems, especially when used offshore.
Even with their limited effectiveness and many drawbacks, the guar (and guar derivatives), and HEC type viscosifiers are commonly used as sweeps and carriers; they are economical to use and, until the present invention, there has been nothing better with which to replace them.
Our commonly-owned previous patent, Kaiser et al, U.S. Pat. No. 6,201,050, which is hereby incorporated by reference herein in its entirety, discloses a viscous breakable gel additive carrier for mixing with ion containing materials, including dry powder based and calciferous materials, which in its uniform homogeneous gel form, prevents separation and settling of the additives prior to mixing, and upon mixing with the ion containing materials liquefies and becomes totally and evenly miscible to allow easy and precise mixing. The gel includes formulations of selected additives thoroughly mixed with a cross-linked polyacrylic acid gelling agent, an organic chelating agent, and an alkaline electrolyte to produce uniform homogeneous mortars, grouts, stuccos and other compositions. The present invention is distinguished over the previous patent and provides a different formulation of constituents that enhance well drilling, completion and production operations and other uses while greatly increasing the efficiency of the process and significantly lowering cost.
Our commonly-owned previous patent, Kaiser et al, U.S. Pat. No. 6,528,563, which is hereby incorporated by reference herein in its entirety, discloses multi-use homogeneous breakable gelled adhesives and adhesive mastics which can be used “as is” for the installation of various types of tile, including tiles with deeply grooved backs, stone, marble, and other floor and wall coverings, flexible sheet goods, carpet and other uses, and can be mixed with a Portland cement powder to form a powerful latex-modified mortar having the added utility of a crack suppressive adhesive and functioning as a waterproofing membrane. The stabilized gelled adhesive or adhesive mastic prevents the separation and settling of components, and when Portland powdered cement is added, becomes a high strength latex modified mortar. The gelled adhesive or adhesive mastic is usable as a latex modified dry-set mortar. With the addition of Portland cement and silica sand, the gel will break and become a free-flowing liquid with additives which allow precise quantitation and easy mixing to produce a homogeneous latex modified thinset mortar that assumes the texture of a trowelable thinset mortar as more Portland cement/silica sand is added. The present invention is distinguished over the previous patent and provides a different formulation of constituents that enhance well drilling, completion and production operations and other uses while greatly increasing the efficiency of the process and significantly lowering cost.
Nguyen et al, U.S. Pat. No. 6,794,340 discloses a method for removing drill cuttings from wellbores and drilling fluids using a reversible cross-linkable polymer and an encapsulated crosslink activator which delays the cross-linking. It is submitted that any downhole residual materials from the preferred polysaccharide polymer formulations taught by Nguyen et al that are not returned to the surface during the wash or sweep processes will leave significant deposits in the pore throats and interstices of the adjacent subterranean strata. Commonly referred to as “snot,” this material may be difficult or impossible to remove even with repeated flushing of the strata. The present invention, on the other hand, does not require encapsulation and the gel when mixed with the breaker produces virtual instantaneous liquefaction, or breaking, of the final gel into a free-flowing liquid.
Allan et al, U.S. Pat. No. 6,838,418 discloses a fracturing fluid comprising polar base, 0.1-5.0% of a mid or lower molecular weight (about 500,000) polyacrylate, an activator for ionizing the polyacrylate to a hygroscopic state, and a breaker in an amount of 0.1-1.0% wt, wherein the breaker is NaCl or KCl. The polyacrylate is a polyacrylic acid polymer cross linked with polyalkenyl ethers or di-vinyl glycol. The breaker is preferably encapsulated to allow it to be transported to the fracture site easily, and the fluid is emulsified by adding liquid Carbon dioxide CO2 or N2 and a surfactant under high pressure to the fluid stream near the wellhead.
Unlike the Allen et al patent, the base concentrate of the present invention comprises a mixture of from about 80% to about 91.8% by weight of a buffered water solution containing acidic and alkaline ions and having a pH above about pH 3, and from about 0.4% to about 16.24% of a polyacrylate; and a second or activator solution containing a mixture of water, an amine cross-linking agent, and a nonionic surfactant. The cross-linking agent in the activator preferably comprises diisopropanolamine, and the breaker material comprises ammonium persulfate, although calcium chloride, sodium chloride, or potassium chloride may also be used. The present invention, uses more effective multi-valent ions for breaking, is cross linked with different chemicals, requires no encapsulation of the breaker, and no emulsification or surfactants are required. The present invention also provides acid/base buffering molecules that compensate for significant swings in other components and/or additives required or unknowingly present as constituents of the source water. It also enhances the speed of mixing subsequent additions, decreases the quantities of ingredients required, and provides for more rapid and cleaner breaking of the gel when desired while leaving no gel residue.
One of the major problems encountered in well fracturing is that the water used is typically from a source other than municipal water supplies and therefore is of limited uniformity. The source water may be high in natural salts and chlorides such as calcium and its salts, as well as magnesium, potassium, etc. Whether single ions or large particulates, the type and quantities of dissolved solids in the source water are critical to successful fracturing,
The source water may also commonly be stockpiled in “roll-off” boxes, which are large containers, brought to each well site to store the massive quantities of liquids, gels, etc. to be used during the completion process. Fracturing alone may require availability of even 4,000,000 gallons water/gel/etc. often pumped into the well in a matter of minutes. Commonly 8′×10′×42′ carbon steel “boxes” with a capacity to 500 barrels are used. These containers are usually leased, brought to each site as needed, and then quickly moved on to the next drill site. Each “roll-off” box is different, much depending on prior use. The interior of the container may not have been cleaned well after its last use thus may contain high or low pH residuals or other contaminants. The interior may also be rusty and therefore be a source of iron complexes, i.e. rust, which may prevent gel formation or break or liquify stored gel. Another factor affecting the water used in well fracturing is that the transportation equipment including tanker trucks, high and low pressure pump trucks, and other hauling and handling devices may be contaminated with composition altering contaminants.
Unlike many prior art well fracturing formulations, the present invention overcomes problems with the source water by utilizing a combination of acid and alkaline electrolytes and an amine crosslinking agent that are formulated in ratios within a particular critical range which not only serves to elevate the pH of the source water, but also provides acid/base buffering molecules which are essential to attain effective and consistent results vital to effective gel formation and maintenance in field use. This feature produces a buffering solution that compensates for significant swings in other components and/or additives required or unknowingly present as constituents of the source water and achieves superior results that are incapable of being achieved by percentage ranges that are taught by prior art formulations. It also enhances the speed of mixing the subsequent additions, decreases the quantities of ingredients required, and provides for more rapid and cleaner breaking of the gel when desired while leaving no gel residue. In some cases, depending on the source water makeup, simply significantly increasing the quantity of “Base Concentrate” and “Activator” utilized in the mixture (described hereinafter) will provide desired gelling.